Matthew Perry

When he had the chance to audition for the role of Chandler Bing, he narrowly avoided having to skip the Friends audition because he was committed to another series called LAX 2194 that even FOX, the show's own network, called "the worst thing we've ever seen in our lives," Perry joked.

Lisa Kudrow got a little nostalgic with her former Friends costar Matthew Perry when he filled in as guest host on Piers Morgan Tonight Friday.

The pair reminisced about how much they enjoyed working on the iconic sitcom, which ended nine years ago, and Perry, 43, admitted, "If I had a time machine, I would like to go back to 2004 and not have stopped."

Kudrow agreed: "If it were up to us, you know, individually, then yes. I would keep going … We had a lot of fun."

When the Glee star died at 31 of a toxic mix of heroin and alcohol, he was just two months out of treatment for substance abuse. Post-rehab, the actor looked healthy and happy, attending a hockey game with his girlfriend, Lea Michele, dining out with friends and attending a photo call for the next season of his FOX hit.

But addiction experts say that the immediate period after rehab is one of tremendous vulnerability.

"Newly sober people are more fragile than before they became addicts," says Bob Forrest, a California-based certified drug and alcohol counselor.

At 24, Matthew Perry landed a role that would utterly change his life – and help define a generation: Chandler Bing on Friends.

Along with his five castmates, his face was suddenly on everything from calendars to coffee mugs, and his salary ballooned to $1 million an episode. As his sardonic alter ego might have put it, "Could he be any more famous?"

But behind the scenes, Perry struggled with a serious alcohol problem. Then, after a 1997 Jet Ski accident, a doctor prescribed him Vicodin and said, "'Here, take this.' I did, and I felt better than I ever felt in my entire life," Perry says. "I had a big problem with pills and alcohol, and I couldn't stop."

For a decade, Matthew Perry was living an actor's dream: he had an iconic role as sardonic Chandler Bing on the beloved No. 1 sitcom Friends and a salary that reached $1 million an episode.

But behind the scenes, Perry was struggling. "I had a big problem with alcohol and pills and I couldn't stop," he tells PEOPLE in an exclusive new cover story. "Eventually things got so bad that I couldn't hide it, and then everybody knew."

In the clip (watch it below), Aniston knocks Perry's door to get some tips from her former castmate, who also has co-hosted the show.

"We haven't actually seen each other in like a really long time, 8 years. ... You really should have called," said a nervous Perry, who looked on sheepishly as their mutual pal and former costar Courteney Cox emerges from his house after an obvious sleepover.

After nearly three decades of television and film experience under his belt, Matthew Perry admits at times he has had a been there, done that feeling when it comes to work.

But the former Friends star, whose new NBC comedy Go On premieres Tuesday night, can't help smiling when he talks about his new costars.

"I'm jaded because I'm old, but these guys are literally singing all day long and having a good time," Perry, 43, tells PEOPLE. "Everybody is really funny and really smart and really happy to be there. We all know that we're a part of something that is at least is aspiring to be cool and different."

The annual TV upfronts have started in Manhattan, with the networks announcing their fall lineups and tossing sardine-size video clips into the open mouths of assembled advertisers and media people.

The big news out of NBCs presentation Monday is that The Voice, the network's standout hit, will be making more use of those wonderful swivel chairs. Yes, America, you will get to see more of Christina Aguilera swiveling, and you will be glad of it.

As to the actual new lineup ... well, NBC has had its problems with programming. Even the mightily promoted Smash, after a heavenly opening, sputtered. Its star, Katharine McPhee, was brought out not once but twice to perform at the upfront, but her show won't be back until midseason.